Seems to me that if the sender of a text message knows the recipient of it is driving, he or she should be at least partially held liable in an accident resulting from the recipient's answering the message or looking at it while driving. Of course, on the other hand, the recipient of the message is directly and fully liable for choosing to look at or answer a text message while driving should doing so result in an accident (which is not an accident at all, but something that possibly could have been prevented had the recipient not responded to the text message but kept their attention totally on what they were doing while driving--thus the harm done is the direct result of the removal of attention to one's driving resulting from the decision to examine the incoming text message.)
While driving, it seems to me highly dangerous to answer any text or phone message without pulling off the highway to do so.